Many new emerging applications require the use of ultra-low power consumption solutions inside a chip. This will allow them to be incorporated into devices that operate from a small non-chargeable battery for very long periods without the need to frequently charge the battery. For example, wearable, mobile devices and IoT (Internet of Things) devices and the like, may require an ultra-low power solution.
Reducing the operating voltage is the most effective method for power reduction and working at the Near/Sub-threshold voltage domain can save 70-80% from the dynamic power consumption and 50-60% from the leakage power. Near/Sub-threshold technology is a way of operating the transistors in their weak inversion state where the transistors are never fully turned on. When operating in the Near/Sub-threshold region, the transistor state varies between being fully turned off and partially turned on.
When operating in the Near/Sub-threshold region, transistors operate at a near or lower voltage than their threshold voltage (known as VT) and by such operation the transistor uses less power. During Near/Sub-threshold voltage operation, both dynamic power (which is caused by a logic change) and static power (which is consume all the time) are reduced. Dynamic power is a ratio of the operating voltage by a power of two, and static power is a ratio of the operating voltage, therefore reducing the operating voltage of the device to a Near/Sub-threshold voltage level will reduce power dramatically (in the range of 3-5× then a comparable solution working at standard voltage).
One of the major limiting factors for using Near/Sub-threshold technology is the low performance of the transistors at a very low voltage and due to this limitation the usage of Near/Sub-threshold technology in commercial chips is very limited.
The second limiting factor is the low yield problem for chips which are working at the Near/Sub-threshold domain due to the VT variation between the P-ch and N-ch transistors which increases when the voltage goes down.
Various methods and implementations for the Near/Sub-threshold technology exist today, those methods focus only on power reduction and not on the optimal way to use this technology for a given power per performance required by a specific application or how to improve the final product yield.
There is still a need for Near/Sub Threshold technology methods which optimizes power consumption while still meeting the performance requirements for a specific product or application and also ensures high yield for high volume production parts.